Sparse Code Multiple Access (SCMA) is a recently developed multiple user access scheme for telecommunication systems. In SCMA, multiple streams of data bits are encoded, each using a respective codebook made up of multiple codewords. Each codeword is transmitted on one or more sub-carriers of a block of SCMA sub-carriers.
When transmission occurs in a downlink direction from a network side component to one or more User Equipment (UEs), a superposition of the codewords on the block of sub-carriers is transmitted by the network side component. When transmission occurs in an uplink direction from two or more synchronized UEs to a network side component, each UE transmits one or more codewords on a subset of sub-carriers of the block of SCMA sub-carriers that are allocated to the UE. The network side component receives signals on the block of SCMA sub-carriers from the two or more UEs that are superposed on air interface channels between the two or more UEs and the network side component.
Performance of SCMA may be affected by various parameters, including codebook design.